Method and apparatus to neutralize replication error and retain primary and secondary synchronization during synchronous replication

ABSTRACT

Techniques are provided for neutralizing replication errors. An operation is executed upon a first storage object and is replicated as a replicated operation for execution upon a second storage object. A first error may be received for the replicated operation. Instead of transitioning to an out of sync state and aborting the operation, a wait is performed until a result of the attempted execution of the operation is received. If the first error is the same as a second error returned for the operation, then the operation and replicated operation are considered successful and a synchronous replication relationship is kept in sync. If the first error and the second error are different errors, then an error response is returned for the operation and the synchronous replication relationship is transitioned to out of sync.

RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S.application Ser. No. 16/288,469, filed on Feb. 28, 2019, titled “METHODAND APPARATUS TO NEUTRALIZE REPLICATION ERROR AND RETAIN PRIMARY ANDSECONDARY SYNCHRONIZATION DURING SYNCHRONOUS REPLICATION,” which isincorporated herein by reference.

BACKGROUND

Many storage systems may implement data replication and/or otherredundancy data access techniques for data loss protection andnon-disruptive client access. For example, a first computing device maybe configured to provide clients with primary access to data storedwithin a first storage device and/or other storage devices. A secondcomputing device may be configured as a backup for the first computingdevice in the event the first computing device fails. Data may bereplicated from the first computing device to the second computingdevice. In this way, the second computing device can provide clientswith access to replicated data in the event the first computing devicefails.

One type of replication is asynchronous replication. When the firstcomputing device receives an operation from a client device, the firstcomputing device transmits a replication of the operation to the secondcomputing device for execution. Irrespective of whether the secondcomputing device has executed the replicated operation, the firstcomputing device will transmit an acknowledgment of successfulperformance of the operation to the client device once the firstcomputing device has executed the operation.

Another type of replication is synchronous replication, which provides agreater level of data protection guarantees, such as a zero recoverypoint objective (RPO). This is because the first computing device doesnot transmit the acknowledgment until the operation has been executed bythe first computing device and the replicated operation has beenexecuted or acknowledged by the second computing device. In this way,two copies of data and/or metadata resulting from the operation aremaintained before the client receives acknowledgment that the operationwas successful.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in which an embodiment of the invention may be implemented.

FIG. 2 is a component block diagram illustrating an example data storagesystem in which an embodiment of the invention may be implemented.

FIG. 3 is a flow chart illustrating an example method for neutralizingreplication errors.

FIG. 4A is a component block diagram illustrating an example system forneutralizing replication errors, where a success response is generatedbased upon a first error and a second error being the same error.

FIG. 4B is a component block diagram illustrating an example system forneutralizing replication errors, where an error response is generatedbased upon a first error and a second error being different errors.

FIG. 5 is a component block diagram illustrating an example system forhandling replication errors.

FIG. 6 is an example of a computer readable medium in which anembodiment of the invention may be implemented.

FIG. 7 is a component block diagram illustrating an example computingenvironment in which an embodiment of the invention may be implemented.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

In asynchronous replication, incremental changes to a storage object,such as a volume, a file, a directory, a defined set of files ordirectories, a file system, or a storage virtual machine comprising aplurality of volumes stored across one or more nodes of a cluster, arereplicated from the storage object to a replicated storage object. Insynchronous replication, when an operation is received from a clientdevice (e.g., a write operation targeting the storage object), theoperation is split to create a replicated operation that is areplication of the operation. The operation is executed upon the storageobject, such as by a first computing device managing the storage object.The replicated operation is executed upon the replicated storage object,such as by a second computing device managing the replicated storageobject. The operation is not acknowledged to the client device as beingcomplete until both the operation and the replicated operation havesuccessfully been executed upon the storage object and the replicatedstorage object.

Accordingly, methods and/or systems are provided herein that improvesynchronous replication by dynamically allocating and recycling filerange locks, neutralizing replication errors without going out of sync,and handling misaligned holes and writes beyond an end of file during aquick reconcile process. Synchronous replication may be implemented forfirst storage object hosted by a first computing environment (e.g., afirst node) and a second storage object hosted by a second computingenvironment (e.g., a second node) as a replica of the first storageobject. A synchronous replication relationship is established betweenthe first storage object and the second storage object.

In an embodiment of dynamically allocating and recycling file rangelocks, overlapping writes can occur where multiple parallel writes(e.g., inflight write operations not yet fully executed and replicated)target overlapping ranges of the first storage object. The order thatthe overlapping writes are executed upon the first storage object needsto be maintained when replicated to the second storage object. Otherwisea divergence will occur between the first storage object and the secondstorage object. Order of execution is preserved at the second storageobject by serializing the overlapping writes using a range lock. Asingle range lock is used per storage object (per file). However, thisdoes not scale well for storage environments having a large number offiles. Accordingly, the present system can dynamically allocate andrecycle range locks as needed in order to scale to storage environmentshaving large numbers of files.

An overlapping write manager is used to maintain the order of executionof writes between the first storage object and the second storage objectusing range locks. In an example, an overlapping write manager allocatoris setup and used to pre-allocate a percentage of a total number ofoverlapping write managers to be available for managing overlappingwrites targeting files of the first computing environment (e.g., thefirst storage object managed by the first node) and replicated toreplicate files stored by the second computing environment (e.g., thesecond storage object managed by the second node).

In an embodiment of pre-allocating overlapping write managers, when anoutstanding allocation of overlapping write managers (e.g., overlappingwrite managers being used by incoming writes) grows beyond a threshold(e.g., 10%, 20%, etc.), then additional overlapping write managers areallocated for use by overlapping writes.

A mapping is used to track allocated overlapping write managers. Themapping comprises file handles of files for which allocated overlappingwrite managers have ben pre-allocated (drawn) from the overlapping writemanager allocator, and thus are available for use to obtain range locksfor corresponding files. File handles are used as a key to the mapping.When I/O to a file is received, the mapping is search using a filehandle of the file to see if an overlapping write manager for the filehandle of the file is already allocated. For example, the mapping isevaluated using a file handle of a file targeted by an incoming write todetermine whether an overlapping write manager is already allocated forthe file handle.

If the overlapping write manager is already allocated, then theoverlapping write manager is utilized to acquire a range lock for arange of the file to be modified by the incoming write. The incomingwrite is serially executed upon the file and is serially replicated to areplicated file using the range lock (e.g., the replicate filemaintained as a replica of the file). In this way, the range lock isused to block overlapping writes targeting at least a portion of therange of the file targeted by the incoming write (e.g., overlappingreplicated writes targeting the replicated file). If the mapping doesnot comprise an entry for the file handle, then there is nopre-allocated overlapping write manager for the file handle. Thus, a newoverlapping write manager is allocated by the overlapping write managerallocator. The incoming write uses the new overlapping write manager toobtain a range lock for the range of the file for serial execution andreplication. A new entry is created within the mapping to track the newoverlapping write manager allocated for the file handle.

In an embodiment, overlapping write managers are recycled to returnoverlapping write managers back to the overlapping write managerallocator. For example, once the incoming write operation has completedexecution upon the file and completed replication to the replicatedfile, the range lock is released. The overlapping write manager becomesavailable for use by other writes. If no outstanding writes having rangelocks for the file, then the entry is removed from the mapping for theoverlapping write manager and the overlapping write manager isdeallocated. If there are no outstanding writes having references to theoverlapping write manager (e.g., there are no writes attempting toacquire range locks for the file), then the entry is removed from themapping for the overlapping write manager and the overlapping writemanager is deallocated.

During recycling of overlapping write managers, an entry for anoverlapping write manager is removed from the mapping and theoverlapping write manager is returned to a free pool of pre-allocatedoverlapping write managers. In an embodiment of recycling overlappingwrite managers, overlapping write managers are deallocated until anumber of allocated overlapping write managers is less than a threshold,which reduces an allocation percentage. In an embodiment, the totalnumber of overlapping write managers is maintained within the pool. Anumber of allocated overlapping write managers is reduced from the poolsuch as during recycling to free computing resources (e.g., recyclingstops when an allocation percentage is low such as 20%).

In an embodiment, replication errors for synchronous replication areneutralized. A first storage object is maintained by a first computingenvironment and a second storage object is maintained by a secondcomputing environment as a replica of the first storage object. Anoperation is received while the first storage object and the secondstorage object are in a synchronous replication state. The operation isexecuted upon the first storage object and is replicated as a replicatedoperation for execution upon the second storage object.

The second computing environment may return a first error for thereplicated operation. The first error may indicate that the replicatedoperation did not successfully execute, such as due to a file systemerror (e.g., the replicated operation targets a file handle that isstale because a targeted file has been delete; the replicated operationwould increase a size of a file beyond a supported file size; etc.).Upon receiving the first error for the replicated operation, theoperation is refrained from being aborted from being executed upon thefirst storage object (e.g., the operation would normally be aborted dueto the first error). The first storage object and the second storageobject are refrained from being transitioned to an out of sync statebased upon the first error. The synchronous replication would normallybe transitioned to an out of sync state, and thus a zero recovery pointobjective (RPO) provided by synchronous replication would be disrupted.

Synchronous replication waits until both the operation and thereplicated operation have finished. A second error may be received forthe operation from the first computing environment. If the first errorand the second error are the same error, then the replicated operationis deemed to be successfully completed so that the synchronousreplication is maintained and not transitioned to the out of sync state.Accordingly, the first storage object and the second storage object aremaintained in a synchronous replication state. The same error isreturned to the client device as the operation was a failure from clientdevice's perspective. However, if the first error and the second errorare different errors, the first storage object and the second storageobject could be different (inconsistent) due to different results fromthe different errors. The synchronous replication state will betransitioned to an out of sync state. The client is responded to withthe error from the first (primary) computing environment.

In an embodiment of handling situations where no response is returnedfor the replicated operation, the second computing environment maintainsa failed ops cache of failed operations and error codes for each failedoperation. Sequence numbers assigned to replicated operations are usedas a key for the failed ops cache. If the first computing environmentdoes not receive a response for the replicated operation, then a retryof the replicated operation with a same sequence number will betransmitted to the second computing environment. If a sequence number ofthe retry replicated operation is specified by an entry/mapping withinthe failed ops cache as mapping the replicated operation to an errorcode, then the error code is transmitted to the first computingenvironment. This is because the second computing environment alreadyattempted to execute the replicated operation and the error code wasgenerated. Thus, since the retry replicated operation is a retry of thereplicated operation (e.g., the second computing environment may haveattempted to return the error code for the replicated operation but anetwork failure cause the first computing device to not receive theerror code and thus the first computing environment retried thereplicated operation after a timeout period), the retry replicatedoperation is not executed and the error code is returned.

In an embodiment of performing a quick reconcile operation, misalignedholes and writes beyond an end of a storage object (e.g., an end of fileof a file) are handled. The quick reconcile operation is performed if anoperation fails to execute upon a first storage object and a replicatedoperation of the operation succeeds at executing upon a second storageobject maintained as a replica of the first storage object. The quickreconcile operation is executed to read “old” data from the firststorage object and write the “old” data from the first storage object tothe second storage object (e.g., effectively undoing the execution ofthe replicated operation) so that the storage objects are consistent.When the data is being read from the first storage object, the datacould have misaligned holes that do not start and/or end at an alignedoffset, such as at 4 kb aligned offsets. Synchronous replication, suchas the quick reconcile operation, cannot handle the misaligned holesbecause holes can only be punched at aligned offsets and lengths, suchas at the 4 kb aligned offsets. Further, if the failed operation was awrite operation to a range beyond an end of file, then the quickreconcile operation cannot read that data from the first storage object.

Accordingly, the present system is capable of handling misaligned holesand writes beyond an end of file (e.g., an end of a storage object). Inan example of handling misaligned holes, a read operation is executedagainst the first storage object at an offset and length of a writeoperation during a quick reconcile process to reconcile the firststorage object and the second storage object. For example, the writeoperation was successfully replicated to the second storage object butfailed to execute against the first storage object. Thus, the readoperation is performed to read “old” data from the first storage objectto write to the second storage object so that the storage objects areconsistent.

A read response of the read operation is evaluated to determine whetherthe read response has a misaligned hole. If the read response comprisesthe misaligned hole (e.g., a first I/O vector entry is a hole and astart offset is not 4 kb aligned or a last I/O vector entry is a holeand an end offset is not 4 k aligned), then the read request is modifiedto align the misaligned hole.

If the misaligned hole is due to the first I/O vector entry having amisaligned start offset, then the start offset is rounded down to ablock size used to store the second storage object (e.g., to 4 kb). Ifthe misaligned hole is due to the last I/O vector entry having amisaligned end offset, then the end offset is rounded up to a nearestaligned block size value (e.g., to 4kb) as a new length. The new readresponse (e.g., the “old” data read from the first storage object andmodified to address any misaligned holes) is replicated to the secondstorage object.

In an example of handling writes beyond an end of file, the readresponse of the read operation is evaluated to determine whether anerror code or length of read data indicates whether the read data isbeyond an end of the first storage object. If the read response iscompletely beyond the end of the first storage object, then a truncatecommand with a size of the first storage object is executed upon thesecond storage object. A volume barrier or dependency graph is used toensure that the truncate command is serially executed with respect toother inflight replicated operations targeting the second storageobject.

If the read response is partially beyond the end of the first storageobject, then data from a start offset until the end of file is read fromthe first storage object and replicated to the second storage object. Atruncate command having a size of the first storage object is executedupon the second storage object. In an example, the replication of thedata and the truncate command can be combined as a single commandtransmitted to the second computing environment for execution upon thesecond storage object. A flag or field within the command can be used toindicate that the truncate command is to be performed after the writingthe replicate data. A volume barrier or dependency graph is used toensure that the command such as the truncate command is seriallyexecuted with respect to other inflight replicated operations targetingthe second storage object.

To provide for neutralizing replication errors, FIG. 1 illustrates anembodiment of a clustered network environment 100 or a network storageenvironment. It may be appreciated, however, that the techniques, etc.described herein may be implemented within the clustered networkenvironment 100, a non-cluster network environment, and/or a variety ofother computing environments, such as a desktop computing environment.That is, the instant disclosure, including the scope of the appendedclaims, is not meant to be limited to the examples provided herein. Itwill be appreciated that where the same or similar components, elements,features, items, modules, etc. are illustrated in later figures but werepreviously discussed with regard to prior figures, that a similar (e.g.,redundant) discussion of the same may be omitted when describing thesubsequent figures (e.g., for purposes of simplicity and ease ofunderstanding).

FIG. 1 is a block diagram illustrating the clustered network environment100 that may implement at least some embodiments of the techniquesand/or systems described herein. The clustered network environment 100comprises data storage systems 102 and 104 that are coupled over acluster fabric 106, such as a computing network embodied as a privateInfiniband, Fibre Channel (FC), or Ethernet network facilitatingcommunication between the data storage systems 102 and 104 (and one ormore modules, component, etc. therein, such as, nodes 116 and 118, forexample). It will be appreciated that while two data storage systems 102and 104 and two nodes 116 and 118 are illustrated in FIG. 1, that anysuitable number of such components is contemplated. In an example, nodes116, 118 comprise storage controllers (e.g., node 116 may comprise aprimary or local storage controller and node 118 may comprise asecondary or remote storage controller) that provide client devices,such as host devices 108, 110, with access to data stored within datastorage devices 128, 130. Similarly, unless specifically providedotherwise herein, the same is true for other modules, elements,features, items, etc. referenced herein and/or illustrated in theaccompanying drawings. That is, a particular number of components,modules, elements, features, items, etc. disclosed herein is not meantto be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, In an embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while In an embodiment a clustered network caninclude data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more host devices 108, 110 which maycomprise, for example, client devices, personal computers (PCs),computing devices used for storage (e.g., storage servers), and othercomputers or peripheral devices (e.g., printers), are coupled to therespective data storage systems 102, 104 by storage network connections112, 114. Network connection may comprise a local area network (LAN) orwide area network (WAN), for example, that utilizes Network AttachedStorage (NAS) protocols, such as a Common Internet File System (CIFS)protocol or a Network File System (NFS) protocol to exchange datapackets, a Storage Area Network (SAN) protocol, such as Small ComputerSystem Interface (SCSI) or Fiber Channel Protocol (FCP), an objectprotocol, such as S3, etc. Illustratively, the host devices 108, 110 maybe general-purpose computers running applications, and may interact withthe data storage systems 102, 104 using a client/server model forexchange of information. That is, the host device may request data fromthe data storage system (e.g., data on a storage device managed by anetwork storage control configured to process I/O commands issued by thehost device for the storage device), and the data storage system mayreturn results of the request to the host device via one or more storagenetwork connections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, cloud storage (e.g., a storage endpoint may bestored within a data cloud), etc., for example. Such a node in theclustered network environment 100 can be a device attached to thenetwork as a connection point, redistribution point or communicationendpoint, for example. A node may be capable of sending, receiving,and/or forwarding information over a network communications channel, andcould comprise any device that meets any or all of these criteria. Oneexample of a node may be a data storage and management server attachedto a network, where the server can comprise a general purpose computeror a computing device particularly configured to operate as a server ina data storage and management system.

In an example, a first cluster of nodes such as the nodes 116, 118(e.g., a first set of storage controllers configured to provide accessto a first storage aggregate comprising a first logical grouping of oneor more storage devices) may be located on a first storage site. Asecond cluster of nodes, not illustrated, may be located at a secondstorage site (e.g., a second set of storage controllers configured toprovide access to a second storage aggregate comprising a second logicalgrouping of one or more storage devices). The first cluster of nodes andthe second cluster of nodes may be configured according to a disasterrecovery configuration where a surviving cluster of nodes providesswitchover access to storage devices of a disaster cluster of nodes inthe event a disaster occurs at a disaster storage site comprising thedisaster cluster of nodes (e.g., the first cluster of nodes providesclient devices with switchover data access to storage devices of thesecond storage aggregate in the event a disaster occurs at the secondstorage site).

As illustrated in the clustered network environment 100, nodes 116, 118can comprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise network modules 120, 122 and disk modules 124, 126. Networkmodules 120, 122 can be configured to allow the nodes 116, 118 (e.g.,network storage controllers) to connect with host devices 108, 110 overthe storage network connections 112, 114, for example, allowing the hostdevices 108, 110 to access data stored in the distributed storagesystem. Further, the network modules 120, 122 can provide connectionswith one or more other components through the cluster fabric 106. Forexample, in FIG. 1, the network module 120 of node 116 can access asecond data storage device by sending a request through the disk module126 of node 118.

Disk modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, disk modules 124, 126 communicate with the data storage devices128, 130 according to the SAN protocol, such as SCSI or FCP, forexample. Thus, as seen from an operating system on nodes 116, 118, thedata storage devices 128, 130 can appear as locally attached to theoperating system. In this manner, different nodes 116, 118, etc. mayaccess data blocks through the operating system, rather than expresslyrequesting abstract files.

It should be appreciated that, while the clustered network environment100 illustrates an equal number of network and disk modules, otherembodiments may comprise a differing number of these modules. Forexample, there may be a plurality of network and disk modulesinterconnected in a cluster that does not have a one-to-onecorrespondence between the network and disk modules. That is, differentnodes can have a different number of network and disk modules, and thesame node can have a different number of network modules than diskmodules.

Further, a host device 108, 110 can be networked with the nodes 116, 118in the cluster, over the storage networking connections 112, 114. As anexample, respective host devices 108, 110 that are networked to acluster may request services (e.g., exchanging of information in theform of data packets) of nodes 116, 118 in the cluster, and the nodes116, 118 can return results of the requested services to the hostdevices 108, 110. In an embodiment, the host devices 108, 110 canexchange information with the network modules 120, 122 residing in thenodes 116, 118 (e.g., network hosts) in the data storage systems 102,104.

In an embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. In an example, a disk array can include alltraditional hard drives, all flash drives, or a combination oftraditional hard drives and flash drives. Volumes can span a portion ofa disk, a collection of disks, or portions of disks, for example, andtypically define an overall logical arrangement of file storage on diskspace in the storage system. In an embodiment a volume can comprisestored data as one or more files that reside in a hierarchical directorystructure within the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the clustered network environment 100, the host devices 108, 110 canutilize the data storage systems 102, 104 to store and retrieve datafrom the volumes 132. In this embodiment, for example, the host device108 can send data packets to the network module 120 in the node 116within data storage system 102. The node 116 can forward the data to thedata storage device 128 using the disk module 124, where the datastorage device 128 comprises volume 132A. In this way, in this example,the host device can access the volume 132A, to store and/or retrievedata, using the data storage system 102 connected by the storage networkconnection 112. Further, in this embodiment, the host device 110 canexchange data with the network module 122 in the node 118 within thedata storage system 104 (e.g., which may be remote from the data storagesystem 102). The node 118 can forward the data to the data storagedevice 130 using the disk module 126, thereby accessing volume 132Bassociated with the data storage device 130.

It may be appreciated that neutralizing replication errors may beimplemented within the clustered network environment 100. In an example,operations may be executed at node 116 and replayed at node 118. It maybe appreciated that neutralizing replication errors may be implementedfor and/or between any type of computing environment, and may betransferrable between physical devices (e.g., node 116, node 118, adesktop computer, a tablet, a laptop, a wearable device, a mobiledevice, a storage device, a server, etc.) and/or a cloud computingenvironment (e.g., remote to the clustered network environment 100).

FIG. 2 is an illustrative example of a data storage system 200 (e.g.,102, 104 in FIG. 1), providing further detail of an embodiment ofcomponents that may implement one or more of the techniques and/orsystems described herein. The data storage system 200 comprises a node202 (e.g., nodes 116, 118 in FIG. 1), and a data storage device 234(e.g., data storage devices 128, 130 in FIG. 1). The node 202 may be ageneral purpose computer, for example, or some other computing deviceparticularly configured to operate as a storage server. A host device205 (e.g., 108, 110 in FIG. 1) can be connected to the node 202 over anetwork 216, for example, to provide access to files and/or other datastored on the data storage device 234. In an example, the node 202comprises a storage controller that provides client devices, such as thehost device 205, with access to data stored within data storage device234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other similar media adaptedto store information, including, for example, data (D) and/or parity (P)information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 242. The data storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) optimization technique to optimize areconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202, such as a network storagecontroller, can respond to host device requests to manage data on thedata storage device 234 (e.g., or additional clustered devices) inaccordance with these host device requests. The operating system 208 canoften establish one or more file systems on the data storage system 200,where a file system can include software code and data structures thatimplement a persistent hierarchical namespace of files and directories,for example. As an example, when a new data storage device (not shown)is added to a clustered network system, the operating system 208 isinformed where, in an existing directory tree, new files associated withthe new data storage device are to be stored. This is often referred toas “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and adapters 210,212, 214 for storing related software application code and datastructures. The processors 204 and adapters 210, 212, 214 may, forexample, include processing elements and/or logic circuitry configuredto execute the software code and manipulate the data structures. Theoperating system 208, portions of which are typically resident in thememory 206 and executed by the processing elements, functionallyorganizes the storage system by, among other things, invoking storageoperations in support of a file service implemented by the storagesystem. It will be apparent to those skilled in the art that otherprocessing and memory mechanisms, including various computer readablemedia, may be used for storing and/or executing application instructionspertaining to the techniques described herein. For example, theoperating system can also utilize one or more control files (not shown)to aid in the provisioning of virtual machines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to ahost device 205 over a network 216, which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. The host device 205 (e.g., 108, 110 of FIG. 1) may be ageneral-purpose computer configured to execute applications. Asdescribed above, the host device 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the node 202 to access information requested by the hostdevice 205 (e.g., access data on a storage device managed by a networkstorage controller). The information may be stored on any type ofattached array of writeable media such as magnetic disk drives, flashmemory, and/or any other similar media adapted to store information. Inthe example data storage system 200, the information can be stored indata blocks on the disks 224, 226, 228. The storage adapter 214 caninclude input/output (I/O) interface circuitry that couples to the disksover an I/O interconnect arrangement, such as a storage area network(SAN) protocol (e.g., Small Computer System Interface (SCSI), iSCSI,hyperSCSI, Fiber Channel Protocol (FCP)). The information is retrievedby the storage adapter 214 and, if necessary, processed by the one ormore processors 204 (or the storage adapter 214 itself) prior to beingforwarded over the system bus 242 to the network adapter 210 (and/or thecluster access adapter 212 if sending to another node in the cluster)where the information is formatted into a data packet and returned tothe host device 205 over the network 216 (and/or returned to anothernode attached to the cluster over the cluster fabric 215).

In an embodiment, storage of information on disk arrays 218, 220, 222can be implemented as one or more storage volumes 230, 232 that arecomprised of a cluster of disks 224, 226, 228 defining an overalllogical arrangement of disk space. The disks 224, 226, 228 that compriseone or more volumes are typically organized as one or more groups ofRAIDs. As an example, volume 230 comprises an aggregate of disk arrays218 and 220, which comprise the cluster of disks 224 and 226.

In an embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, whereas directories may be implemented asspecially formatted files in which information about other files anddirectories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume corresponds to at least a portion of physical storagedevices whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalstorage device locations, such as some available space from each of thedisks 224, 226, and/or 228. It will be appreciated that since a virtualvolume is not “tied” to any one particular storage device, a virtualvolume can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, Qtrees 235, and files 240. Among otherthings, these features, but more particularly LUNS, allow the disparatememory locations within which data is stored to be identified, forexample, and grouped as data storage unit. As such, the LUNs 238 may becharacterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In an embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumesstored on a data storage device, a target address on the data storagedevice can be used to identify one or more LUNs 238. Thus, for example,when the node 202 connects to a volume 230, 232 through the storageadapter 214, a connection between the node 202 and the one or more LUNs238 underlying the volume is created.

In an embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the one or more LUNs 238.

It may be appreciated that neutralizing replication errors may beimplemented for the data storage system 200. It may be appreciated thatneutralizing replication errors may be implemented for and/or betweenany type of computing environment, and may be transferrable betweenphysical devices (e.g., node 202, host device 205, a desktop computer, atablet, a laptop, a wearable device, a mobile device, a storage device,a server, etc.) and/or a cloud computing environment (e.g., remote tothe node 202 and/or the host device 205).

One embodiment of neutralizing replication errors is illustrated by anexemplary method 300 of FIG. 3 and further described in conjunction withsystem 400 of FIGS. 4A and 4B and system 500 of FIG. 5. A first storageobject 404 (e.g., a file, a logical unit number, a storage virtualmachine of a plurality of volumes, a directory, a volume, a consistencygroup of any arbitrary or defined grouping of data, etc.) may bemaintained by a first computing environment (e.g., a node, a controller,a cloud computing environment, a cluster of nodes, software as aservice, etc.), as illustrated by FIG. 4A. A second storage object 406may be maintained by a second computing environment. The first storageobject 404 and the second storage object 406 may have a synchronousreplication relationship where I/O directed to the first storage object404 are intercepted and split into replicated I/O that ARE replicated tothe second storage object 406. In this way, when an operation, such as awrite command, targeting the first storage object 404 is received, theoperation is executed upon the first storage object 404 and isreplicated and executed upon the second storage object 406.

Synchronous replication can provide a zero recovery point objective(RPO) because an operation is not acknowledged as complete until theoperation has successfully executed upon the first storage object 404and has successfully been replicated to the second storage object 406.Unfortunately, various types of errors, such as file system errors, cancause the synchronous replication relationship to be transitioned to anout of sync state, thus losing the zero RPO benefits of being in asynchronous state. However, such errors can occur for both the operationand the replicated operation such that the first storage object 404 andthe second storage object 406 are still consistent and have the samedata. In these situations, it would be beneficial to not transition thesynchronous replication relationship to the out of sync state.

Accordingly, as provided herein, replication errors are handled in amanner such that the synchronous replication relationship is retained inthe in-sync state when both an operation and a replicated operation havethe same error. At 302, an operation 408 is executed upon the firststorage object 404 and is replicated as a replicated operation 412 forexecution upon the second storage object 406 by a replication component402 based upon the synchronous replication relationship being in anin-sync state. The replication component 402 may receive a first error414 related to the execution of the replicated operation 412 upon thesecond storage object 406 by the second computing environment. Undernormal operation, the replication component 402 would abort theoperation 408 and transition the synchronous replication relationshipout of sync based upon the first error 414, thus losing the benefitssuch as zero RPO provided by synchronous replication. However, thereplication component 402 is instead configured to refrain from abortingthe operation 408 and refrain from transitioning to an out of sync statein response to receiving the first error 414, at 304. Instead, thereplication component 402 waits until the operation 408 has completed.

The replication component 402 receives a second error 410 related to theexecution of the operation 408 upon the first storage object 404 by thefirst computing environment. The replication component 402 compares 416the first error 414 and the second error 410 to determine whether thefirst error 414 and the second error 410 relate to the same error ordifferent errors, at 306. Because synchronous replication is replicating“live” (not yet acknowledged back to hosts/clients) I/O, file systemerrors can be encountered such that both the operation 408 and thereplicated operation 412 would likely encounter the same file systemerror. In an example, the file system error may relate to the operation408 and the replicated operation 412 having stale file handles (e.g.,file handles of already deleted files). In another example, the filesystem error may relate to the operation 408 and the replicatedoperation 412 attempting to increase a file size of a file beyond asupported file system size.

At 308, the replication component 402 determines that the first error414 and the second error 410 relate to the same type of error based uponthe comparison 416. Accordingly, the replication component 402 maintains418 the synchronous replication relationship in an in-sync synchronousreplication state based upon the first error 414 and the second error410 relating to the same type of error. The replication component 402acknowledges 420 the operation 408 and the replicated operation 412 assuccessfully completing based upon the first error 414 and the seconderror 410 relating to the same type of error. This is because the sameresult (same error) occurred for both the operation 408 and thereplicated operation 412, and thus the first storage object 404 and thesecond storage object 406 will have the same state and be consistent.

FIG. 4B illustrates the replication component 402 executing a secondoperation 430 upon the first storage object 404 and replicating thesecond operation 430 as a replicated second operation 434 for executionupon the second storage object 406. The replication component 402receives a third error 436 related to the execution of the replicatedsecond operation 434 upon the second storage object 406 by the secondcomputing environment. Under normal operation, then replicationcomponent 402 would abort the second operation 430 and transition thesynchronous replication relationship out of sync based upon the thirderror 436, thus losing the benefits such as zero RPO provided bysynchronous replication. However, the replication component 402 isinstead configured to refrain from aborting the operation and refrainfrom transitioning to an out of sync state in response to receiving thethird error 436. Instead, the replication component 402 waits until thesecond operation 430 has completed.

The replication component 402 receives a fourth error 432 related to theexecution of the second operation 430 upon the first storage object 404by the first computing environment. The replication component 402compares 438 the third error 436 and the fourth error 432 to determinewhether the third error 436 and the fourth error 432 relate to the sameerror or different errors. Based upon the replication component 402determining that the third error 436 and the fourth error 432 aredifferent types of errors, the replication component 402 transitions 440the synchronous replication relationship to an out-of-sync state. Thereplication component 402 returns an error response 442 to the secondoperation 430. This is because the first storage object 404 and thesecond storage object 406 could potentially be in different states(e.g., comprise different data) and be inconsistent with respect to oneanother because the third error 436 and the fourth error 432 aredifferent.

FIG. 5 illustrates a system 500 for handling replication errors. A firstdevice 502 manages a first storage object 504 (e.g., a file, adirectory, a logical unit number, a volume, a storage virtual volume ofa plurality of volumes, a consistency group of an arbitrary or definedset of data, etc.) having a replication relationship with a secondstorage object 508 managed by a second device 506. Based upon thereplication relationship such as a synchronous replication relationship,operations executed upon the first storage object 504 are replicated asreplicated operation for execution upon the second storage object 508.When the first device 502 transmits a replicated operation to the seconddevice 506, then first device 502 may start a timer. If the timer timesout before a response is received from the second device 506 for thereplicated operation, the first device 502 will retry sending thereplicated operation to the second device 506. Sequence numbers may beassigned to replicated operations by the first device 502 in order touniquely identify and distinguish between replicated operations (e.g., asequence number may be a monotonically increasing number that isassigned to operations, wherein a sequence number of an operation isalso assigned to a replicated operation of that same operation). If areplicated operations is retried, then the same sequence number is used.

The second device 506 is configured to maintain a failed ops cache 514used to track failed replicated operations that the second device 506was unable to successfully execute (e.g., replicated operations thatreturned an error in response to the second device 506 executing thereplicated operations upon the second storage object 508). The seconddevice 506 may track sequence numbers of failed replicated operationswithin the failed ops cache 514. In this way, when an incomingreplicated operation is received, the second device 506 can use thefailed ops cache 514 to determine whether the incoming replicatedoperation is a retry of a failed replicated operation.

In an example, the second device 506 receives an incoming replicatedoperation 510 comprising a sequence number 512. The second device 506evaluates the failed ops cache 514 to determine whether the sequencenumber 512 is specified within the failed ops cache 514. For example,the second device 506 determines that the sequence number 512 is mappedto an error code 516 within the failed ops cache 514. Because thesequence number 512 is mapped to the error code 516, the second device506 can determine that the incoming replication operation 510 is a retryof a failed replicated operation having the same sequence number 512,and that the error code 516 was generated when execution of the failedreplicated operation upon the second storage object 508 was attempted.Accordingly, the second device 506 does not execute the incomingreplicated operation 510 and instead returns the error code 516, thesequence number 512, and/or other information to the first device 502 asa response to the incoming replicated operation 510.

In an example, a timer is used to clean up entries within the failed opscache 514, such as after a protocol timeout of an operation so thatafter the protocol timeout occurs, a host/client is returned with anerror. Thus, the first device 502 will only retry operations until theprotocol timeout occurs. For example, an entry is removed from thefailed ops cache 514 based upon the protocol timer timing out for anoperation corresponding to the entry (e.g., the entry has a sequencenumber of the operation). In this way, an error is transmitted to aclient device for the operation.

Still another embodiment involves a computer-readable medium 600comprising processor-executable instructions configured to implement oneor more of the techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 6, wherein the implementationcomprises a computer-readable medium 608, such as a compactdisc-recordable (CD-R), a digital versatile disc-recordable (DVD-R),flash drive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 606. This computer-readable data 606, such asbinary data comprising at least one of a zero or a one, in turncomprises a processor-executable computer instructions 604 configured tooperate according to one or more of the principles set forth herein. Insome embodiments, the processor-executable computer instructions 604 areconfigured to perform a method 602, such as at least some of theexemplary method 300 of FIG. 3, for example. In some embodiments, theprocessor-executable computer instructions 604 are configured toimplement a system, such as at least some of the exemplary system 400 ofFIGS. 4A-4C and/or at least some of the exemplary system 500 of FIG. 5,for example. Many such computer-readable media are contemplated tooperate in accordance with the techniques presented herein.

FIG. 7 is a diagram illustrating an example operating environment 700 inwhich an embodiment of the techniques described herein may beimplemented. In one example, the techniques described herein may beimplemented within a client device 728, such as a laptop, tablet,personal computer, mobile device, wearable device, etc. In anotherexample, the techniques described herein may be implemented within astorage controller 730, such as a node configured to manage the storageand access to data on behalf of the client device 728 and/or otherclient devices. In another example, the techniques described herein maybe implemented within a distributed computing platform 702 such as acloud computing environment (e.g., a cloud storage environment, amulti-tenant platform, etc.) configured to manage the storage and accessto data on behalf of the client device 728 and/or other client devices.

In yet another example, at least some of the techniques described hereinare implemented across one or more of the client device 728, the storagecontroller 730, and the distributed computing platform 702. For example,the client device 728 may transmit operations, such as data operationsto read data and write data and metadata operations (e.g., a create fileoperation, a rename directory operation, a resize operation, a setattribute operation, etc.), over a network 726 to the storage controller730 for implementation by the storage controller 730 upon storage. Thestorage controller 730 may store data associated with the operationswithin volumes or other data objects/structures hosted within locallyattached storage, remote storage hosted by other computing devicesaccessible over the network 726, storage provided by the distributedcomputing platform 702, etc. The storage controller 730 may replicatethe data and/or the operations to other computing devices so that one ormore replicas, such as a destination storage volume that is maintainedas a replica of a source storage volume, are maintained. Such replicascan be used for disaster recovery and failover.

The storage controller 730 may store the data or a portion thereofwithin storage hosted by the distributed computing platform 702 bytransmitting the data to the distributed computing platform 702. In oneexample, the storage controller 730 may locally store frequentlyaccessed data within locally attached storage. Less frequently accesseddata may be transmitted to the distributed computing platform 702 forstorage within a data storage tier 708. The data storage tier 708 maystore data within a service data store 720, and may store clientspecific data within client data stores assigned to such clients such asa client (1) data store 722 used to store data of a client (1) and aclient (N) data store 724 used to store data of a client (N). The datastores may be physical storage devices or may be defined as logicalstorage, such as a virtual volume, LUNs, or other logical organizationsof data that can be defined across one or more physical storage devices.In another example, the storage controller 730 transmits and stores allclient data to the distributed computing platform 702. In yet anotherexample, the client device 728 transmits and stores the data directly tothe distributed computing platform 702 without the use of the storagecontroller 730.

The management of storage and access to data can be performed by one ormore storage virtual machines (SMVs) or other storage applications thatprovide software as a service (SaaS) such as storage software services.In one example, an SVM may be hosted within the client device 728,within the storage controller 730, or within the distributed computingplatform 702 such as by the application server tier 706. In anotherexample, one or more SVMs may be hosted across one or more of the clientdevice 728, the storage controller 730, and the distributed computingplatform 702.

In one example of the distributed computing platform 702, one or moreSVMs may be hosted by the application server tier 706. For example, aserver (1) 716 is configured to host SVMs used to execute applicationssuch as storage applications that manage the storage of data of theclient (1) within the client (1) data store 722. Thus, an SVM executingon the server (1) 716 may receive data and/or operations from the clientdevice 728 and/or the storage controller 730 over the network 726. TheSVM executes a storage application to process the operations and/orstore the data within the client (1) data store 722. The SVM maytransmit a response back to the client device 728 and/or the storagecontroller 730 over the network 726, such as a success message or anerror message. In this way, the application server tier 706 may hostSVMs, services, and/or other storage applications using the server (1)716, the server (N) 718, etc.

A user interface tier 704 of the distributed computing platform 702 mayprovide the client device 728 and/or the storage controller 730 withaccess to user interfaces associated with the storage and access of dataand/or other services provided by the distributed computing platform702. In an example, a service user interface 710 may be accessible fromthe distributed computing platform 702 for accessing services subscribedto by clients and/or storage controllers, such as data replicationservices, application hosting services, data security services, humanresource services, warehouse tracking services, accounting services,etc. For example, client user interfaces may be provided tocorresponding clients, such as a client (1) user interface 712, a client(N) user interface 714, etc. The client (1) can access various servicesand resources subscribed to by the client (1) through the client (1)user interface 712, such as access to a web service, a developmentenvironment, a human resource application, a warehouse trackingapplication, and/or other services and resources provided by theapplication server tier 706, which may use data stored within the datastorage tier 708.

The client device 728 and/or the storage controller 730 may subscribe tocertain types and amounts of services and resources provided by thedistributed computing platform 702. For example, the client device 728may establish a subscription to have access to three virtual machines, acertain amount of storage, a certain type/amount of data redundancy, acertain type/amount of data security, certain service level agreements(SLAs) and service level objectives (SLOs), latency guarantees,bandwidth guarantees, access to execute or host certain applications,etc. Similarly, the storage controller 730 can establish a subscriptionto have access to certain services and resources of the distributedcomputing platform 702.

As shown, a variety of clients, such as the client device 728 and thestorage controller 730, incorporating and/or incorporated into a varietyof computing devices may communicate with the distributed computingplatform 702 through one or more networks, such as the network 726. Forexample, a client may incorporate and/or be incorporated into a clientapplication (e.g., software) implemented at least in part by one or moreof the computing devices.

Examples of suitable computing devices include personal computers,server computers, desktop computers, nodes, storage servers, storagecontrollers, laptop computers, notebook computers, tablet computers orpersonal digital assistants (PDAs), smart phones, cell phones, andconsumer electronic devices incorporating one or more computing devicecomponents, such as one or more electronic processors, microprocessors,central processing units (CPU), or controllers. Examples of suitablenetworks include networks utilizing wired and/or wireless communicationtechnologies and networks operating in accordance with any suitablenetworking and/or communication protocol (e.g., the Internet). In usecases involving the delivery of customer support services, the computingdevices noted represent the endpoint of the customer support deliveryprocess, i.e., the consumer's device.

The distributed computing platform 702, such as a multi-tenant businessdata processing platform or cloud computing environment, may includemultiple processing tiers, including the user interface tier 704, theapplication server tier 706, and a data storage tier 708. The userinterface tier 704 may maintain multiple user interfaces, includinggraphical user interfaces and/or web-based interfaces. The userinterfaces may include the service user interface 710 for a service toprovide access to applications and data for a client (e.g., a “tenant”)of the service, as well as one or more user interfaces that have beenspecialized/customized in accordance with user specific requirements,which may be accessed via one or more APIs.

The service user interface 710 may include components enabling a tenantto administer the tenant's participation in the functions andcapabilities provided by the distributed computing platform 702, such asaccessing data, causing execution of specific data processingoperations, etc. Each processing tier may be implemented with a set ofcomputers, virtualized computing environments such as a storage virtualmachine or storage virtual server, and/or computer components includingcomputer servers and processors, and may perform various functions,methods, processes, or operations as determined by the execution of asoftware application or set of instructions.

The data storage tier 708 may include one or more data stores, which mayinclude the service data store 720 and one or more client data stores.Each client data store may contain tenant-specific data that is used aspart of providing a range of tenant-specific business and storageservices or functions, including but not limited to ERP, CRM, eCommerce,Human Resources management, payroll, storage services, etc. Data storesmay be implemented with any suitable data storage technology, includingstructured query language (SQL) based relational database managementsystems (RDBMS), file systems hosted by operating systems, objectstorage, etc.

In accordance with one embodiment of the invention, the distributedcomputing platform 702 may be a multi-tenant and service platformoperated by an entity in order to provide multiple tenants with a set ofbusiness related applications, data storage, and functionality. Theseapplications and functionality may include ones that a business uses tomanage various aspects of its operations. For example, the applicationsand functionality may include providing web-based access to businessinformation systems, thereby allowing a user with a browser and anInternet or intranet connection to view, enter, process, or modifycertain types of business information or any other type of information.

In an embodiment, the described methods and/or their equivalents may beimplemented with computer executable instructions. Thus, In anembodiment, a non-transitory computer readable/storage medium isconfigured with stored computer executable instructions of analgorithm/executable application that when executed by a machine(s)cause the machine(s) (and/or associated components) to perform themethod. Example machines include but are not limited to a processor, acomputer, a server operating in a cloud computing system, a serverconfigured in a Software as a Service (SaaS) architecture, a smartphone, and so on). In an embodiment, a computing device is implementedwith one or more executable algorithms that are configured to performany of the disclosed methods.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), electrically erasable programmable read-only memory(EEPROM) and/or flash memory, compact disk read only memory (CD-ROM)s,CD-Rs, compact disk re-writeable (CD-RW)s, DVDs, cassettes, magnetictape, magnetic disk storage, optical or non-optical data storage devicesand/or any other medium which can be used to store data.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

1-20. (canceled)
 21. A method, comprising: receiving a replicatedoperation from a first node that executed an operation from a clientupon a first storage object and generated the replicated operation as areplica of the operation for a second node to execute upon a secondstorage object; attempting, by the second node, to execute thereplicated operation upon the second storage object; and in response toreceiving an error associated with execution of the replicatedoperation, determining that the replicated operation is a failedreplicated operation and tracking a sequence number of the failedreplicated operation within a failed ops cache.
 22. The method of claim21, wherein the sequence number is assigned to both the operation andthe replicated operation.
 23. The method of claim 21, comprising:returning an error code for an incoming replicated operation having thesequence number mapped within the failed ops cache to the error code.24. The method of claim 21, wherein the tracking comprises: mapping thesequence number to an error code within the failed ops cache.
 25. Themethod of claim 21, comprising: returning an error code for an incomingreplicated operation having the sequence number mapped within the failedops cache to the error code, wherein the incoming replicated operationis determined to be a retry of the failed replicated operation trackedwithin the failed ops cache.
 26. The method of claim 21, comprising:determining that an incoming replicated operation is a retry of thefailed replicated operation tracked within the failed ops cache basedupon the incoming replicated operation being assigned the sequencenumber tracked within the failed ops.
 27. The method of claim 21,wherein the tracking comprises: creating an entry, for the sequencenumber, within the failed ops cache.
 28. The method of claim 21, whereinthe tracking comprises: creating an entry, mapping the sequence numberto an error code returned for the failed replicated operation, withinthe failed ops cache.
 29. The method of claim 21, wherein the trackingcomprises: creating an entry, mapping the sequence number to an errorcode returned for the failed replicated operation, within the failed opscache; and removing the entry within the failed ops cache based upon aprotocol timer timing out.
 30. The method of claim 21, comprising:tracking sequence numbers of failed replicated operations targeting thesecond storage object within the failed ops cache, wherein an error codeis returned for an incoming replicated operation having the sequencenumber mapped within the failed ops cache to the error code.
 31. Acomputing device comprising: a memory comprising machine executable codefor performing a method; and a processor coupled to the memory, theprocessor configured to execute the machine executable code to cause theprocessor to: receive a replicated operation from a first node thatexecuted an operation from a client upon a first storage object andgenerated the replicated operation as a replica of the operation for asecond node to execute upon a second storage object; attempt, by thesecond node, to execute the replicated operation upon the second storageobject; and in response to receiving an error associated with executionof the replicated operation, determine that the replicated operation isa failed replicated operation and tracking a sequence number of thefailed replicated operation within a failed ops cache.
 32. The computingdevice of claim 31, wherein the sequence number is assigned to both theoperation and the replicated operation.
 33. The computing device ofclaim 31, wherein the machine executable code causes the processor to:return an error code for an incoming replicated operation having thesequence number mapped within the failed ops cache to the error code.34. The computing device of claim 31, wherein the machine executablecode causes the processor to: mapping the sequence number to an errorcode within the failed ops cache.
 35. The computing device of claim 31,wherein the machine executable code causes the processor to: return anerror code for an incoming replicated operation having the sequencenumber mapped within the failed ops cache to the error code, wherein theincoming replicated operation is determined to be a retry of the failedreplicated operation tracked within the failed ops cache.
 36. Thecomputing device of claim 31, wherein the machine executable code causesthe processor to: determine that an incoming replicated operation is aretry of the failed replicated operation tracked within the failed opscache based upon the incoming replicated operation being assigned thesequence number tracked within the failed ops.
 37. A non-transitorymachine readable medium comprising instructions for performing a method,which when executed by a machine, causes the machine to: receive areplicated operation from a first node that executed an operation from aclient upon a first storage object and generated the replicatedoperation as a replica of the operation for a second node to executeupon a second storage object; attempt, by the second node, to executethe replicated operation upon the second storage object; and in responseto receiving an error associated with execution of the replicatedoperation, determine that the replicated operation is a failedreplicated operation and tracking a sequence number of the failedreplicated operation within a failed ops cache.
 38. The non-transitorymachine readable medium of claim 37, wherein the instructions cause themachine to: create an entry, for the sequence number, within the failedops cache.
 39. The non-transitory machine readable medium of claim 37,wherein the instructions cause the machine to: create an entry, mappingthe sequence number to an error code returned for the failed replicatedoperation, within the failed ops cache.
 40. The non-transitory machinereadable medium of claim 37, wherein the instructions cause the machineto: create an entry, mapping the sequence number to an error codereturned for the failed replicated operation, within the failed opscache; and remove the entry within the failed ops cache based upon aprotocol timer timing out.